Qadgop The Mercotan has been a long-time favorite of mine, even though I still automatically look for that u after the capital Q! 
There are so many of you with unique names that it would take me all night long to list them all.
I haven’t seen Tequila Mockingbird in ages, but her name always made me smile.
I too like the “play on words” such as Shirley Ujest and Sue Dunhym.
Quasi
Thanks for the suggestion!
http://boards.straightdope.com/sdmb/showthread.php?threadid=147733
Thank you sweetie. 
Honey;
I like you on bagels, english muffins, and toast
Butter and honey, is quite yummy,
While bagels and lox,
filled with snot, is not.
Honey…
I am very sad that Don’t poke the bear, Dad! isn’t around more. That was my all-time favorite.
Eats Crayons always makes me giggle. And so does That Guy With Pants. I’d never noticed Ferret Herder until this thread but that’s a hoot, too.
There are many other good ones, but (a) I’ve listed them before and (b) my brain is too addled today to recall them.
Hey now! I resent the fact that mine’s cool. 
I just changed my username this weekend; got my change-of-name sig up there in my previous post. Finally thought of something good for a username. I have pet ferrets so I do know what it’s like, plus it describes my life sometimes - all the frustration of herding cats, with twice the hyperactivity.
You people have no taste whatsoever.
And hitting the submit button will post you every time. My favorite was of course ‘aha’
One more for fireunderpantsboobs.
I also like Running with scissors.
I also like Rue DeDay, although I just realized a few weeks ago that he was, in fact, a man. I read it as a pun, but it stuck in my head as Rue, which makes me think of Rue McLanahan (sp?), so I pictured him as a grey-haired woman.
Sorry, Rue.
I also like Shabadu. (hey, Joey Jo-Jo!)
I always liked Mmmmm…forbiden doughnut (please forgive the spelling) and Green Bean
fireunderpantsboobs is pretty cool too.
You know what was a good one? nothemama
I have quite a few personal faves. Have to mention TheLoadedDog and RueDeDay. Also Cougarfang and the likes of Mirrored Indigo Shadows, and Thylacine. Loads of others – I usually pop up, say “What a cool name!” at th’ time, then vanish off again.
Oh yeah. I also like “Yapping Poodle,” but I do feel like smacking the poster every time I see the name. Heh heh. I’m intrigued that someone would deliberately choose a name that is practically synonymous with extreme annoyance. Gutsy, and interesting. So it’s up there on my favorites list.
CrankyAsAnOldMan noticed me!! I’ve hit the big top! Not bad for a guy who posts randomly eh? For what its worth, I read mostly. I get on the board everyday and see what people have to say, but I dont really have much to talk about. lol. Thanks to everyone who enjoyed my seldom-seen name!
kplmonkeypants is good, too
That Guy: Eats Crayons cracks me up too!
I have a bunch of favorite names, but never really got around to compiling a list of them all… here’s some I remember off the top of my head:
TheLoadedDog
Zappo
Broken Doll
pezpunk
ResIpsaLoquiitor
SkipMagic
thinksnow
Mullinator
Silver Fire
And I know some people have said in the past that they like my name… I don’t know, though. It’s unique, is all I can say about it.
F_X
Am I the only one who thinks that Czarcasm is a hilarious username?